1. Convert to string

const input = 123; console.log(input + ''); // '123' console.log(String(input)); // '123' console.log(input.toString()); // '123'

2. Convert to number

const input = '123'; console.log(+input); // 123 console.log(Number(input)); // 123 console.log(parseInt(input)); // 123

3. Convert to boolean

const input = 1; // Solution 1 - Use double-exclamation (!!) to convert to boolean console.log(!!input); // true // Solution 2 - Pass the value to Boolean() console.log(Boolean(input)); // true

4. Problem with the string `'false'`

const value = 'false'; console.log(Boolean(value)); // true console.log(!!value); // true // The best way to check would be, console.log(value === 'false');

5. null vs undefined

null is a value, whereas undefined is not.null is like an empty box, and undefined is no box at all.
ex.,

const fn = (x = 'default value') => console.log(x); fn(undefined); // default value fn(); // default value fn(null); // null

When null is passed, the default value is not taken, whereas when undefined or nothing is passed the default value is taken.

6. Truthy and Falsy values

Falsy values - false, 0, "" (empty string), null, undefined, & NaN.

Truthy values - "false", "0", {} (empty object), & [] (empty array)

7. What changes can be made with `const`

const is used when the value does not change. ex,

const name = 'Codedrops'; name = 'Codedrops.tech'; // Error const list = []; list = [1]; // Error const obj = {}; obj = { name: 'Codedrops' }; // Error

But it can be used to update value in previously assigned arrays/objects references

const list = []; list.push(1); // Works list[0] = 2; // Works const obj = {}; obj['name'] = 'Codedrops'; // Works

8. Difference between double equal and triple equal

// Double equal - Converts both the operands to the same type and then compares console.log(0 == '0'); // true // Triple equal - Does not convert to same type console.log(0 === '0'); // false

9. Better way to accept arguments

function downloadData(url, resourceId, searchText, pageNo, limit) {} downloadData(...); // need to remember the order

Simpler way to do this-

function downloadData( { url, resourceId, searchText, pageNo, limit } = {} ) {} downloadData( { resourceId: 2, url: "/posts", searchText: "programming" } );

10. Rewriting normal function as arrow function

const func = function() { console.log('a'); return 5; }; func();

can be rewritten as

const func = () => (console.log('a'), 5); func();

11. Return an object/expression from arrow function

const getState = (name) => ({name, message: 'Hi'});

12. Convert a set to an array

const set = new Set([1, 2, 1, 4, 5, 6, 7, 1, 2, 4]); console.log(set); // Set(6) {1, 2, 4, 5, 6, 7} set.map((num) => num * num); // TypeError: set.map is not a function

To convert to an array

const arr = [...set];

13. Check if a value is an arr

const arr = [1, 2, 3]; console.log(typeof arr); // object console.log(Array.isArray(arr)); // true

14. Object keys are stored in insertion order

const obj = { name: "Human", age: 0, address: "Earth", profession: "Coder", }; console.log(Object.keys(obj)); // name, age, address, profession

Objects maintain the order in which the keys were created.

15. Nullish coalescing operator

const height = 0; console.log(height || 100); // 100 console.log(height ?? 100); // 0

Nullish coalescing operator (??) returns the right-hand side value only if the left-hand side value is undefined or null

16. map()

It is a utility function which helps in applying a function on every element of the array.
It returns a new array, which contains the values returned from that applied function. ex.,

const numList = [1, 2, 3]; const square = (num) => { return num * num } const squares = numList.map(square); console.log(squares); // [1, 4, 9]

Here, the function square is applied to every element. i.e., 1, 2, 3.

The returned value of that function is returned as the new element value.

17. try..catch..finally - Real example

const getData = async () => { try { setLoading(true); const response = await fetch( "https://jsonplaceholder.typicode.com/posts" ); // if error occurs here, then all the statements //in the try block below this wont run. // Hence cannot turn off loading here. const data = await response.json(); setData(data); } catch (error) { console.log(error); setToastMessage(error); } finally { setLoading(false); // Turn off loading irrespective of the status. } }; getData();

18. Destructuring

const response = { msg: "success", tags: ["programming", "javascript", "computer"], body: { count: 5 }, }; const { body: { count, unknownProperty = 'test' }, } = response; console.log(count, unknownProperty); // 5 'test'

Thanks for reading 💙